This invention relates to improved methods for achieving the equilibrium number of phases in multi-component compositions which are useful as catholyte or anolyte materials in batteries. Particularly, it relates to an improved method of lithiating FeS.sub.2 and achieving the equilibrium number of phases in the resultant composition.
Many batteries are known to have undesirable voltage irregularities, e.g., voltage transients ("spikes") occuring upon battery initiation or during battery discharge, voltage fall-off, particularly at the end of a battery's useful life, irreproducibility, etc. Many attempts have been made to improve or eliminate such irregularities.
In commonly assigned patent application Ser. No. 872,718 to Godshall, filed on even date, a very effective solution to this problem is disclosed. It involves using as the anolyte or catholyte composition, one which is in, or which upon battery initiation immediately reaches its equilibrium number of phases and which falls in an invariant (degrees of freedom=0) region of the corresponding metallurgical phase diagram. For the lithium thermal battery, this principle is embodied in the lithiation of the conventional FeS.sub.2 cathode material whereby the prior art catholyte falling into a variable region of the Li/Fe/S phase diagram is replaced by lithiated FeS.sub.2 containing sufficient lithium that it falls in the desired invariant region.
In the mentioned copending application, whose entire contents are incorporated by reference herein, methods are described for carrying out the necessary attainment of the equilibrium number of phases and for modifying the conventional battery materials to prepare compositions falling in the necessary invariant region of the corresponding phase diagram. However, these methods are burdensome, involve difficult to handle materials, necessitate a separate mixing step with the electrolyte-binder mix required to prepare the final catholyte, produced final mixtures which have undesirable storage properties, e.g., exhibit settling behavior causing inhomogeneities, etc. Accordingly, there is a need for an improved method of applying the principles of the mentioned prior art disclosure, particularly, to the lithium thermal battery case.